A Study in Green & Silver
by thequeergiraffe
Summary: The first part of the series: The Brave & The Cunning. Sherlock and John are Hogwarts students forced together despite their differences by the Inter-House Challenge. Post-2nd Wizarding War era, spoilers for Sherlock ep.1
1. Chapter 1

The Inter-House Challenge: also known as the bane of John Watson's existence. He turned the card over in his hands once more- emerald green, the stock heavy- and eyed the spidery silver scrawl on it with more trepidation than seemed reasonable. A lot of other boys were mentoring Slytherins, so why should he be so nervous?

John sat down on the edge of his bed, the card in his hands, and stared at the name written there. If he were honest with himself, he knew he wasn't worried because the boy was a Slytherin, or a pureblood, or wildly wealthy. He was worried because the boy was _Sherlock Holmes_.

John had been aware of Sherlock, on some level, since Sherlock's first day at Hogwarts. John had been a second-year, secure and content with his seat on the Gryffindor bench, and he'd known as soon as he saw Sherlock approach the hat that the wild-haired boy at the front of the room would _not _be joining him. There was some debate, from the people who knew his family (which, considering the Holmes name was one of the oldest in Wizarding lineage, was most everyone), about whether Sherlock would be a Ravenclaw or a Slytherin. The eldest Holmes boy, Mycroft, had been a groomed for the dungeon-dwelling house since infancy, but Sherlock…John had heard odd things about Sherlock. That he was intelligent to the point of near-omniscience. That he had an awful temper and a surly attitude, but he was never pointlessly cruel and seemed to actually enjoy helping people (though, according to the people that knew him, it was not the pleasure of charity but the thrill of the puzzle that drew Sherlock's attention). People wondered…but in the end Sherlock joined his brother (a sixth year, at the time) at the Slytherin table, looking none too pleased. And that was that.

Later, John heard rumors about Sherlock. That he'd helped the headmaster find some secret tunnel that had posed a security risk to the castle. That he'd been in a fight with a couple of other Slytherin boys (the name Sebastian Wilkes came up, among others) because they'd called him a freak. That he'd gotten cheeky with a professor and earned himself a year's worth of weekend detentions. That he'd caught out a group of seventh-years who were (rather cleverly, John thought) cheating on their N.E.W.T.s and reported them at once. Despite being a year and an entire castle apart, John found that he'd heard quite a lot about Sherlock Holmes over the years. Now, as he twirled the green card bearing the boy's name on it between his index fingers, he wondered what Sherlock had heard of him.

x

The Inter-House Challenge had been devised shortly after the "Potter Era", as it was known in Hogwarts history. The idea was simple enough: each student would be given, during their O.W.L. year, a mentor in the form of a sixth-year student. To promote inter-house unity, that mentor would be from a differing house. Easy enough. Most students got on well enough with their mentors (John certainly had, though Hufflepuff Molly Hooper had hardly given him a challenge) and the time was spent companionably enough. During the year, mentor and student would meet occasionally to work on their end-of-year Challenge Project, which could be absolutely anything of their devising so long as the students had worked together on it. The fifth-year student was given an O.W.L. mark for the project; the sixth-year student had to write and turn in a report to the headmaster. Best project of the year won a trophy. Couldn't have been more straightforward.

Except…

John couldn't help but think, as he pressed the card with Sherlock's name on it between his palms, that his mentor project was not going to be straightforward at all. Not in the least.

x

The next morning, an assembly of fifth and sixth year students was called in the Great Hall. It was time for the fifth-years to meet their mentors. John entered the cavernous hall with anxiety sitting like a stone in his stomach. He had to fight the urge to tug at his jumper or smooth his fringe as he crossed the room and went to where he'd seen Sherlock Holmes sitting.

Sherlock, for his part, didn't seem nervous at all. He was pale, certainly, but from what John had seen of him…well, the boy was always pale, the fact only accentuated by the mess of dark unruly curls piled atop his head. As John got closer he noticed there was something very posh about Sherlock's cheekbones and his neatly pressed clothes, which in turn only made him more nervous. Still, John wasn't a Gryffindor for no good reason. He had never let nerves get the best of him before, and he certainly wasn't planning to start anytime soon.

"John Watson," he said, sticking out his hand.

The younger boy eyed him the way someone might look at an unexpected stain on a new dress-shirt. "Yes," he said, his voice surprisingly deep and unsurprisingly brisk, "I'm aware." He made no move to introduce himself, nor did he take John's hand.

John cleared his throat and passed his unwelcome hand over his hair. "Right. Well. I'm your mentor."

"Obviously." Sherlock couldn't have sounded more bored if he tried, John thought.

For a moment they were silent: John, standing awkwardly with his hands clasped behind his back and his mouth pulled into a frown; Sherlock, with his strange-coloured eyes narrowed and sweeping over every inch of John's small frame. Finally, Sherlock broke the silence, drawling, "Well, _John_, you're in luck. I'm not in any need of a mentor. I hereby relieve you of your duties."

"You…what?" John shook his head. "You can't just…well, you have to have a mentor. It's a school rule. You can't just…dismiss me." In truth, he was a little offended. Was he not good enough for Sherlock or something? Certainly he wasn't in prime physical condition (a Quidditch injury and a botched healing had done a number on his shoulder, and he sometimes limped a little from the leg he'd broken as a kid) and maybe he wasn't a genius or some rich prat, but John prided himself on being pretty damn likeable. So what was this Holmes kid's deal?

"I can, and I did," Sherlock said carelessly, turning his attention to the book that sat nested in his lap. He glanced up, just for a moment, and met John's eyes before dropping his gaze back to the back and muttering, "You can't be of any use to me."

"You don't even know me," John said automatically, his left hand twitching. (It was an odd habit of John's, flexing the fingers of his dominant hand whenever he was stressed or worried, but it helped somehow and he'd long since decided that was all that counted.) He straightened his back and lifted his chin defiantly, and Sherlock chuckled.

"All right," Sherlock said, steepling his hands beneath his chin, "I know you're a sixth-year, obviously, and a Gryffindor. I know you've got an older brother and you don't get on very well, possibly because he's a drinker but probably because he's a Muggle and he resents you for being different. You're Muggleborn and not close with your parents, either, I imagine because your family is poor and you habitually argue over money. You like Muggle sport and you wish you were good enough to play for Gryffindor's Quidditch team. You're not, however, so you settle for a summer football league back home. You've got a…dog, yes, not a crup, but it's small. Terrier, I'd say, and you're not overly fond of it either so I'd guess it belongs to your brother. The injury to your shoulder is quite real and probably the reason you'll never play Quidditch in any actual capacity; the injury to your leg mystifies magical healers, but your Muggle doctor thinks it's psychosomatic, the events surrounding it having been quite traumatic to you. He's quite correct, I'm afraid." Smiling smugly, Sherlock stood and tucked his book under his arm. Standing, Sherlock was nearly a foot taller than John, but that didn't stop John from folding his arms over his chest and fixing Sherlock with an unwavering stare. Moving to walk away, Sherlock sighed, "That's enough to be going on, don't you think?"

"And all of that disqualifies me from being your mentor _why_ exactly?"

Sherlock froze in his tracks. He spun slowly and met John's eyes with a ferocity that took the older boy back. "You're exceedingly ordinary," Sherlock said slowly, his jaw clenched, "and not my problem. I've better things to do than babysit a future healer with a psychosomatic limp. Have a lovely day, John, and piss off."

"You're wrong about me," John growled. He didn't know why he cared what this rotten snake thought of him, exactly…only that he _did_ care. Maybe because so much of what Sherlock had said about him was true (unnervingly so) but the fundamentals were completely wrong. At least, John hoped they were wrong. He found that he didn't want Sherlock to think he was ordinary. Because he didn't think Sherlock was ordinary at all; he thought Sherlock was absolutely brilliant (if a bit mad, and rude).

To John's surprise, Sherlock looked him over again and then sighed so loudly John imagined the entire student body had heard him. "Fine," Sherlock spat, tapping his long fingers on his folded arm, "then prove it. Meet me tomorrow evening, just before supper bell, outside the dungeons." He seemed to relax some, though he obviously still didn't think very highly of John, and said, "If anyone asks what you're doing, tell them you're waiting for Sherlock Holmes." And then, to John's astonishment, he actually _winked_ and dashed away, his long legs carrying him across the room and out of the hall in a flash.


	2. Chapter 2

John only had a few minutes after Transfiguration before the supper bell rang, and he spent them pushing through crowded corridors and down towards the dungeons. He'd never gone past the Potions classroom and down the stairwell to the Slytherin common room's entrance before, but…well, there was a first time for everything. He took the stairs slowly, aware of the rapidly cooling air and the equally frosty stares of the students around them. He was beginning to wish he'd left on his woolly jumper (which would have at least covered his now-conspicuous Gryffindor tie) when he spotted Sherlock on the landing at the bottom of the stairs, seemingly engaged in very intense conversation with a silver-haired bloke- who, John noted with a jolt of admiration and surprise, was decked out in the robes of a senior Auror. Unsure of his welcome into what seemed like a rather private and important chat, John hovered on the bottom step until Sherlock glanced up and flashed him a startlingly warm smile, waving him over.

"Who's this?" the Auror asked, agitated.

Sherlock gave him a particularly haughty look. "He's with me," he said simply, his tone broaching no argument.

The Auror wasn't impressed. "Look, Sherlock, this is a very…delicate subject, and we'd do well it keep it-"

"I said he's with me," Sherlock snapped, stepping into the Auror's personal space with a contemptuous glare. "What do you think, Lestrade? That I'm an idiot like all of your little lackeys down at the Ministry? If I say he's with me that means I trust him, and if I trust him that means you'd do well to do the same. I won't work this case without him and you _need _me, isn't that right?"

John could only blink at this exchange and Sherlock's apparent and sudden change of heart (wasn't he "exceedingly ordinary" and not Sherlock's problem that very morning?) as Sherlock and the Auror- Lestrade- stood locked in a silent battle of will.

Finally, Lestrade relented with a sigh. "You're right, Merlin help me. I _do_ need you." He drew a roll of parchments from his robe pocket and thrust them at Sherlock with a grimace. "Take a look at those, would you, and for Merlin's sake _owl me _if you think of anything instead of running off on your own like the great bloody git you are." Sparing one less than friendly glance at John, Lestrade strode up the steps- now empty of students since the supper bell had rung- and away, still muttering under his breath.

John shot a questioning glance at Sherlock.

"Muggle murders," Sherlock sighed, seeming to find the answer sufficient. He pocketed the parchments and began swiftly climbing the stairs, John following at his heels.

"Does the Ministry often get involved in Muggle murder cases?" he asked dubiously.

Sherlock snorted. "Only when they're perpetrated by a witch or wizard." His voice was quiet, but the words seemed to ring ominously through the empty stairwell.

"You mean…"

"Quite right. Muggle authorities seem to think the cases are suicides. But they're wrong, naturally." Sherlock grinned at John, his eyes shining gleefully. "They're murders, John. _Murders._"

John contemplated this for a moment, quietly horrified. A wizard- or witch- murdering Muggles…it was the Wizarding world's worst nightmare all over again. No wonder the Ministry was trying to keep it all under wraps. But then another thought struck him.

"Sherlock," he said slowly, pausing in the corridor outside the Great Hall. "Wait a second. I don't understand…why would someone from the Aurors' office contact _you _in regards to what seems like an extremely sensitive case? Actually, why would they contact you for _any _case?"

Sherlock stopped as well, his expression unreadable. "When we met this morning, how much of what I said about you was correct?"

"Nearly all of it, actually."

"Nearly?" Sherlock's eyebrow quirked.

"Yes, very nearly. And I never did ask _how _you knew all those things," John said, his brow furrowed.

"Nearly?" Sherlock mumbled again, apparently perturbed. Shaking himself from his thoughts, Sherlock took a breath and began, rapidly, "This morning, your jumper and your trainers stood out to me immediately. Secondhand, stained, the fabric of the trainers dulled and the wool of the clearly hand-knit jumper obviously sequestered from some other, ancient article. All hand-me-downs, all Muggle made. So: you're poor, Muggleborn, with an older brother who has passed you down his clothes if the writing on your shoes is anything to go on."

John glanced down at the toes of his trainers, which the incorrigible Harry Watson had decorated with an etching of their last name: "WAT" on one foot, "SON" on the other. "How do you know I didn't do that?" he asked, looking back up.

Sherlock, for whatever reason, looked pleased that John had asked. "Same way I knew about the drinking," Sherlock smiled. "Your hair: short, neatly combed. Your fingernails: tidy, clean, trimmed. Those trousers are carefully pressed despite your having worn them three days straight now; your tie is done up properly and with a perfect dimple. No, you're a fastidious sort of boy; you wouldn't write on your trainers, nor would you treat them, or that wretched jumper, so poorly. Aside from that, you don't show any of the signs of a habitual drinker."

"How could you possibly know about the drinking?"

"I make it a point to study various types of stains and the effects they have on certain fabrics," Sherlock sniffed mysteriously. "Your jumper showed signs of having been dribbled with ale and a certain brand of inexpensive scotch whiskey. Muggle alcohol, I'll add, which tells me that your brother isn't like you; he's not a wizard. Also, if I'm not mistaken, that," Sherlock gestured to a pinkish-brown splotch across the laces of John's right trainer (which wouldn't come out, no matter how desperately John scrubbed) and said, "is a bit of sick, hmm? Sober people don't often vomit upon their own shoes, I've noticed."

John flushed and nodded uncomfortably. "Right, well. I'm sure you can see why I don't get on with my family."

"Well, that and the fact that as soon as I mentioned them this morning you started scowling," Sherlock laughed. "You have a very expressive face." John flushed anew as Sherlock went on, seemingly oblivious, "Let's see. I know about the football because of the grass stains on the sides of your trainers. They're quite new, the stains, so not a product of your brother for once. As far as the injuries go, well: I saw you take the one on the shoulder. I was there, at the try-outs. And I saw your idiot friend damage it irreparably."

"Bill Murray," John winced. "He was just trying to help."

"Hmph. Some help he was." Sherlock shrugged dismissively. "The leg is more interesting. When you came into the hall, I noticed you were limping just a bit. The motion is slight, but…noticeable. However, it quite tellingly disappeared the moment I started insulting you. It's like you'd forgotten all about it. St. Mungo's isn't really equipped to deal with psychiatric maladies, unless they were induced magically, but I'd be willing to bet that your regular, Muggle doctor knows it's psychosomatic. I can't get guess at the source but I'm sure it was traumatic, and with more data-"

"You forgot the dog," John said quickly. He didn't want to talk about his leg, not to this kid he hardly knew. "How'd you know about the dog?"

Sherlock looked, for a moment, as though he wanted to press on and ignore the change of topic…but then he sighed and muttered, "There are a few stray hairs on the hems of your trousers, just at the ankle…but not any higher. So: small dog, but you haven't played with it or held it because there aren't any hairs anywhere else on your clothes. Meaning you don't like the dog. If you liked it you'd have wanted to hold it before coming to school, obviously. People are sentimental that way." Sherlock let a breath and looked down the hall before saying, "Which brings us back to our point. The Ministry comes to me for help because I can see. Everything."

"That was…amazing." And it was. John had never seen anything like it.

Sherlock looked up sharply, his pale eyes wide. "…You think so?"

"Of course it was," John rushed. "It was extraordinary. It was quite…" He faltered, realizing he sounded awestruck. "Extraordinary."

"It wasn't," Sherlock said stiffly. "You said so yourself; I got something wrong. Well, what was it?"

John smiled a little. "I don't have a brother. And…I don't play football."

"Don't have a…No. That's impossible." Sherlock shook his head. "You definitely have an older sibling, I can tell."

"Quite right, I do. A sister."

"A sister!" Sherlock pulled a face. "There's always something. And the football? Maybe your _sister _borrows your trainers to play, hmm?"

"No," John chuckled, "I play rugby. Just for fun, with the boys back home."

"Rugby? But you're tiny!" To John's dark look, Sherlock added, a bit sheepishly, "Well, fit, certainly, but still. Look, don't pretend you're not a touch…impish. You barely come up to my chin and I'm a year below you!"

"I don't care how bloody brilliant you are," John menaced, "you'll not be calling me 'impish' again."

They looked at each other, John glowering and Sherlock smirking, before falling into a fit of laughter.


	3. Chapter 3

"Come along, John," Sherlock commanded breezily, stalking off towards the Slytherin table. John hesitated for a moment before trailing along behind him, ill at ease. It wasn't against school rules to sit at another house's table, not so far as John knew, but…

Slytherin and Gryffindor houses were bitter rivals. And even ignoring that, he'd never seen anyone do this before. The Inter-House Challenge was one thing, but sitting at another house's table for supper seemed like an entirely different hurdle.

Still. There was Sherlock, sliding down on to the bench and gesturing at the table, muttering, "You may as well eat," as he slipped the parchments Lestrade had given him from his pocket and unrolled them carefully. John found that even if he had wanted to (and he wasn't sure he did) he couldn't have possibly said 'no'.

He sat down.

"Don't you eat?" John said, stacking his plate and ignoring the uncongenial looks their table-mates were giving him.

"Not when I'm on a case," Sherlock said distractedly. He had pushed his plate and utensils away and was using the table space as an impromptu desk, cups and dinner rolls holding down the parchments' curling edges. "Bad for thinking."

"Right," John said. He took a few bites of some really delicious lasagne and was just considering mentioning to Sherlock that, actually, the brain needed a certain amount of calories just to function properly (much less _well_) when a big, burly hand slapped down on his shoulder.

"Sherlock!" cried an unfamiliar voice. John glanced up to find a hefty young man standing just behind himself and Sherlock, his other hand on Sherlock's shoulder.

Sherlock looked up querulously before smiling, faintly. "Angelo." His eyes flitted to John and he mumbled, with a small splash of colour gracing his cheeks, "John, this is Angelo. Angelo, John."

"John!" It seemed that Angelo was incapable of speaking in anything less than a boom. "Good to meet you! Any friend of Sherlock's is a friend of mine! This fella here saved my hide; got me out of a suspension, you know!"

With something very close to a gracious smile, Sherlock admitted, "Angelo was accused of stealing from the Potions cabinet. I was able to prove that, on the night in question, he was actually in an entirely different part of the castle engaging in petty vandalism."

"Saved my hide!" Angelo said again, winking. "I'd have been in a mess of trouble."

"You _were _in a mess of trouble, as I recall. Detentions for a month."

"Still," the burly boy sighed, squeezing both of their shoulders. A strange expression passed over his face, suddenly; he looked both stricken and enormously pleased. "But look at me! Interrupting! Here, let me make it up to you!" He yanked his wand from his back pocket and pointed it at one of the floating candles, mumbling an incantation under his breath. The candle swept down and landed on the table between John and Sherlock with a soft thunk. "There we are!" Angelo shouted cheerfully. "More romantic! Don't let me stop you from enjoying your date, boys!"

It took John until Angelo was already several paces away to get his voice back. "I'm not his date!" he said, a bit weakly, glancing worriedly at Sherlock.

But Sherlock was ignoring him, his entire focus settled on the scrolls of parchment spread out on the table. "It seems so random," he whispered, his mouth grim. "The victims. There's no common link."

Perhaps because of Angelo's accusations, John found himself uncomfortably aware of how close he was to Sherlock as he leaned in to look at the scrolls himself. The sight of them, though, swept any thoughts of closeness from his mind and instead left him cold. There were several images, each one almost still enough to be mistaken for Muggle photographs. They were of corpses. "Christ," John breathed, tearing his eyes away to look at Sherlock. If Sherlock was disturbed by the bodies, however, he didn't show it. If anything, the boy seemed annoyed, his fingers tapping out an anxious beat on the tabletop.

"Got anything?" John asked, if only because he couldn't stand sitting there silently, looking at those awful photos. (He hadn't seen a dead body in a long time. Years, in fact. He didn't want to think about the last time he saw a body, though, and a dull ache had begun to throb in his leg.)

"What do you make of this?" Sherlock said, scooping up one of the sheets of parchment and thrusting it at John.

The image showed a crime scene, neatly roped up with blue and white police tape (and every few seconds John could see the slight pulse of police lights in the background). In the center of the roped-off area lay a man, curled on his side, vomit oozing from his mouth. Underneath the image someone had written: _Jeffery Patterson, solicitor, aged 46, Muggle, found at Heathrow Airport. _John swallowed, cleared his throat. "No signs of a struggle," he said, looking back up at Sherlock.

Sherlock's eyes were brilliant, blazing. "Good," he said softly. "What else?"

A little warm from the praise and Sherlock's stare, John looked back at the photo and forced himself to refocus. "Well…that implies that the Muggle police were on the right path, doesn't it? It looks like a suicide."

"Except?"

"Except…" John shook his head. "Except, the odd discoloration here?" He ran his fingernail along the image, tracing the line of the dead man's exposed neck. "I…well, I've not seen it in person before, but doesn't that look like lobalug poisoning to you?"

"It certainly does." Lobalugs, aquatic creatures common to the North Sea, were unknown to Muggles and secreted a sort of poison that was often used by Merpeople and in very rare, very difficult to make potions. "That begs the question: how would a Muggle get hold of something as rare and strictly controlled as lobalug poison?"

Scoffing, John shook his head. "Better to ask what sort of a _wizard _can get his hands on the stuff. It's pretty carefully regulated by the Ministry. If someone wanted to use it for…well, less than good reasons, they'd pretty much have to buy it covertly. Black market."

"Merpeople," Sherlock gasped, his eyes going wide. "Oh, John…Merpeople! Of course! Why didn't I think-" He hopped up suddenly and took John's face in his hands, startling the smaller boy into rigidity. "Oh, I _was _wrong about you! I…I could kiss you!" Taking his hands away, Sherlock clapped them together delightedly and gave a little leap. "Clever, damn clever, and you don't even know why! But that's okay, that's fine. John! I have to…" He trailed off, his eyes far away but blazing. And then, in a flash, he was jogging out of the Great Hall with his robes fluttering behind him, and John was left still sitting on the bench, his cheeks pink, as the few remaining Slytherin diners sniggered around him.


	4. Chapter 4

John only sat there, dumbstruck and staring at the empty doorway, for a few seconds before he too was up and dashing, his sneakers pounding on the castle's stone floors with resounding force. "Sherlock!" he cried, whirling around in search of the younger boy. There: a flash of black, the sound of nice shoes (Sunday shoes, John still called them) tapping away rapidly. "Sherlock!" He flew down the corridor at a speed that would have impressed the boys back home and rounded a corner, finally getting Sherlock in his sights. "Sherlock, you berk! Wait a damn bloody second!"

That worked. Sherlock stopped and turned slowly, his eyebrows drawn together. "John?"

"Who were you expecting?" John panted, his hands on his knees. "The pope?"

Sherlock folded his arms and looked at him with unconcealed suspicion. "What do you want?"

"I want to help," John said gently, his breath back. "With the case, with whatever you've got going on it that funny head of yours, with all of it. I want in."

"You want 'in'." Sherlock's voice was quiet, considering. "John…I don't think-"

"Oh come on, Sherlock! Just…let me help with this one. Just this one. And if you decide you don't need me…" John shrugged as casually as he could manage. God, he hoped Sherlock would need him. He wasn't sure why, not really, but the sudden thrill of doing something real and important and _good _(but also exciting, also strange) made him think he'd never be able to get enough of this.

Sherlock hummed softly. "Could be dangerous."

"The best things usually are," John grinned, and Sherlock returned the smile, if a bit cautiously.

"Okay," Sherlock said after a moment's deliberation (and the word brought a new, wider grin to John's face). "Here are the rules: don't be stupid, do as I say, and don't try to be a hero. Got it?" John nodded, and Sherlock sighed: "Fine. Good. Now, we need to gather some supplies."

x

John was made to wait in the hall, well aware of both the ever-looming curfew that was rapidly closing in and the nasty looks of the Slytherins who passed, for an uncomfortable length of time while Sherlock did God knew what inside the Slytherin dormitories. Eventually Sherlock came out, looking a bit lost in thought and hefting a small rucksack which he thrust at John unceremoniously before jogging back up the stairs. John cursed under his breath and slung the bag over his back before taking off after him.

"Wait, Sherlock!"

Sherlock spun around at the top of the stairs, looking annoyed. "Look, if you can't keep up-"

"I can keep up fine," John growled defensively. "I only thought you might like reminding that it's ten minutes to curfew and we're about to go wandering about the castle without so much as a protection charm over us." He was aware of how sarcastic and irritable he sounded but, well…Sherlock had an odd tendency to bring him to the point of exasperation more quickly than anyone John had previously known.

Sighing, Sherlock held out his hand. At John's perplexed look, he rolled his eyes and drawled, "The rucksack, John. Give it to me."

John slowly obeyed, his eyebrows pulled together, and only let out a small huff of aggrieved amusement as Sherlock snatched the pack away and began to root through it hurriedly. He yanked out a folded bit of parchment, closed the bag, and passed it back off to John before turning his attentions back to the paper. "I solemnly swear," he muttered, wandtip pressed to the sheet, "that I am up to no good." John's eyes went wide as the blank page transformed, revealing what looked like an incredibly detailed map of Hogwarts and the surrounding land.

"Christ on the cross," John swore softly. "How long did it take you to make that?"

"I didn't," Sherlock said, though he sounded pleased with himself anyway. He passed the map to John, who examined it with a slackened jaw. "Nicked it. From the Ministry, actually. Old artifact from the Potter era."

"The Marauders' Map." Meeting Sherlock's eyes, John struggled against his disbelief. "You nicked the bloody _Marauders' _Map."

"Yes, yes," Sherlock sighed, still grinning like the cat that got the canary. "Sing my praises later, if you'd like. We've got work to do. Now, you watch the map and follow me _closely, _understood? I trust you're capable enough of doing that much. I don't think I need to tell you to alert me if someone should begin to cross our path. Now do _please _come on. I've got an appointment with a guest who does not like to be kept waiting." With that and a quick glance at the map, Sherlock surged ahead…and John was helpless to do anything but blink and follow.

x

They actually managed to make it out of the castle (and thus pass unquestioned through the corridors) within curfew, though by scant seconds. John was wary, looking over his shoulder despite the reassuring presence of the map, but Sherlock seemed confident as ever as he took long, graceful strides towards the great lake.

Once John felt mostly sure they weren't being followed, he jogged the small distance to Sherlock's side and took little hopping strides to keep up. "Who's this appointment with, then?" he whispered, a bit breathlessly from the lunging pace.

Sherlock ran a hand through his hair distractedly. "A very dangerous and well-respected entity who will probably prove as useless to me as everyone else." John noted the tense tone and nodded to himself in the late-evening darkness, letting silence fall between them.

When they were within feet of the water's edge Sherlock paused, looking contemplative. "Give me the bag," he demanded. John did as he was told, even though he had to grit his teeth to stop himself telling Sherlock off. It wasn't the time or the place for a lesson in manners, and besides: John was intensely curious as to what was going to happen next. From the open rucksack, Sherlock withdrew something small and silver. It looked like a little egg, and in the darkness John thought he could just make out some sort of inscription on the side. Sherlock also pulled out what looked like a bag of mushy seaweed, which he pocketed, and a tiny dagger, which he slipped-still sheathed- neatly into his sock. "Can never be too careful," he whispered, to John's questioning glance. Seemingly prepared, Sherlock took a deep breath and mussed his hair again. "Okay," he said softly, "I need you to hide. There, in the bushes. Have your wand at ready. Should something happen to me, do _not _come after me, understood? Send up a flare, go back to the castle, and tell Lestrade- when he comes- exactly this: 'The Merpeople are implicitly involved'. Got it?"

"They are?" John gaped.

Sherlock's eyes narrowed. "What? No. Well, I'm not sure. That's the whole point of this, isn't it? If they take me as a hostage it's almost definitive proof of their involvement in the Muggle killings."

"If they…" Shaking his head, John grabbed Sherlock's wrist without thinking. "Sherlock, what are we doing?"

Sherlock wrung his hand free and lifted his chin slightly, sniffing, "Solving the case. You have your options, John. Go and hide or else go back to the castle. Either way, you're not stopping me."

John shifted from one foot to the other, his stomach wrenching. He knew he should go back and inform one of the professors. This had gotten out of hand, surely; Sherlock was just a student! But…if he left the boy's side, for even a moment, who knew what trouble he'd get into? John knew there was no talking him out of this ridiculous encounter, and the thought of using force against him didn't sit well. "Fine, go. I'll be right here." He nodded to the bushes, and even in the darkness he couldn't miss Sherlock's small smile.

"All right, then. Farewell, John." He took a few backwards steps and then turned, bridging the short distance to the water in far too short a time. John watched him go with distinct displeasure before slipping into the bushes, his hand gripping his wand tightly.

Sherlock stooped beside the water, touching his wandtip to the surface and causing a small ripple that began to pulse with bright, purple light. The light faded and for a moment there was nothing, just rustling wind and John's pulse thrumming overloud in his own ears. Then the surface of the water broke, a head and a pair of shoulders appearing and startling John into raising his wand, an incantation on his lips. Sherlock, however, didn't seem distressed. He handed the…creature (was that what a merman looked like?) the small silver egg, seemingly ignorant of the fact that several more heads had begun to push their way out of the water, and then smiled pleasantly as the egg was handed back. The Merpeople were hideous, frankly, with skin the color of raw liver and hair that hung from their heads in slimy clumps. John remembered hearing, as a kid, the stories of sailors who'd been bewitched by mermaids, sirens, whatever you wanted to call them, but if he'd ever considered the validity of those stories he now swiftly dismissed them. No one could look at those disgusting, broken teeth and the algae-covered stones that hung around the Merpeople's gilled necks and feel "bewitched", John was certain.

And that was before they spoke.

John clasped his hands to his ears at the awful sounds the first merman began to make, horrible high-pitched squealing that seemed to worm its way inside his head and rattle in his teeth. If it bothered Sherlock, though, the younger boy didn't express it. After several long, agonizing moments, to John's bewilderment, Sherlock made a wretched whining noise in turn before standing abruptly and striding over to where John was hiding.

"Well," Sherlock said, frowning, "it was a long shot anyway."

"You speak Mermish," John said slowly, standing and rubbing at his temples. The grating sounds of the merman's voice were still ringing in his ears painfully.

"Only a few phrases," Sherlock yawned. He hoisted the egg and sighed, "A gift from my usually loathsome brother. It works as a sort of translator. When I held it to my ear, I could hear the merman's words in English. It's a pity the thing only works one way." He stuffed it back in the rucksack with another deep sigh.

"So?" John followed after Sherlock, who had begun pacing back to the castle in his usual agitated way.

"Like I said, it was a long shot. The Slytherin common room looks into the lake, you know, so I wrote in runes on the window, 'Who is the secret buyer? A friend of King Mydor's wants to know. 9pm. Lakeside. SH'."

John had to laugh at Sherlock's audacity. "A friend of King Mydor's? Really? And I don't suppose you worried that they might look into that." King Mydor headed one of the largest Merpeople colonies in the world, situated dead center in the North Sea.

"I presume they did," Sherlock said, straight-faced. Rolling his eyes at John's sudden amazement, he groaned, "Are you aware you're doing that? Yes, I've met King Mydor. He gave my brother that egg. It was a case, two summers ago. You're still making that face, you know."

Shaking his head to clear away his expression, John mumbled, "Sorry."

"No, no, it's…fine," Sherlock hurried, looking at John with a furrowed brow. "I just…" He shrugged and cleared his throat. "Anyway, that was the chief I was speaking to, at the lake. He told me-"

"Oi!"

Both boys leapt, looking around wildly. There, some ways in the distance, a lamp was swinging to and fro. John could just make out the face of the castle's less than pleasant caretaker, Pontius Filch (who, according to accounts of the Potter era, was a spitting image of his apparently awful grandfather, Argus). "Oh, hell," John grumbled. He didn't have time to say anything else; Sherlock's hand slipped into his and began tugging him incessantly away, the boy hissing, "You were meant to be watching the map, you idiot! Come on!"

They ran; Filch gave chase. John's leg ached something awful, and his lungs burned, but he'd never felt more alive. He wondered if he wasn't a bit delirious, choking back laughter as he tripped after Sherlock, the younger boy's bony fingers still roughly interlocked with his. John expected Sherlock to drag him to the castle but didn't slow as they instead turned towards the forest, the curses of Filch the youngest carrying after them. "Come on, come on!" Sherlock gasped, and then there it was: something John hadn't felt in ages. The bliss of a runner's high. His lungs stopped their perpetual begging for air, his leg quieted, and his body thrummed with newly found chemical endurance. Suddenly he wasn't struggling to keep up with Sherlock; they were running side by side, John matching his longer stride easily and not stopping himself from laughing out loud now.

Sherlock laughed too, a quick barking surprise of a laugh, and then shook his head and panted, "Shh! Come on. We'll lose him soon." They skirted along the edge of the forest until the bobbing lamp in the distance was a mere pinprick of light, and then Sherlock released John's hand (had he really been holding it that whole time?) and slowed to a stop. "Lost him," he grinned, breathless, and John's heart flipped uncomfortably in his chest.


	5. Chapter 5

They made their way back into the castle through a secret passage Sherlock pointed out on the map, one that lead its way down towards the basement dungeons. John didn't much like the idea of working his way up to Gryffindor tower without the map (or Sherlock) but the fact didn't really dampen his good mood. Once they moved the grate that allowed them back into the castle and breathed in the damp, musty air of an abandoned dungeon, John sighed contentedly and said, knocking his shoulder lightly against Sherlock's, "Well, I'll see you tomorrow. Breakfast? If that's okay."

Their eyes had fully adjusted to the darkness, so John could see Sherlock looking at him curiously. "It's barely ten. You're not tired."

John laughed. "No, not really."

"Then why go?" Sherlock started making his way slowly towards the dungeon's old wooden door, his footsteps careful and his voice low as he whispered, "Come with me to my room. We can talk about the case."

"Sherlock," John breathed, suddenly glad for the darkness. "I can't- I mean, I'm not allowed- that is, I'm not-"

"We've been breaking the rules all night," Sherlock smiled, pushing open the door and looking both ways down the hall. "Why stop now?"

John's heart was racing, and not just because of all the running. It shouldn't have been that big of a deal, except…except…

"Come on," Sherlock sighed, taking his hand again, and any argument John had been considering fell away in a long, shuddering breath.

x

At this time of night, the Gryffindor common room was usually packed with students and loud with merriment and rowdiness. Not so with the Slytherin common room, John noted. The room was huge and oddly lit, the lake casting the open space with an eerie green hue, and it was entirely empty of anything except overly rich looking furniture and a million long, green candles.

"Where is everyone?" John mumbled, sticking close to Sherlock.

Sherlock raised in eyebrow. "In their rooms, I suppose. Don't worry, John. You won't be seen."

John flushed but nodded. Leading the way, Sherlock pulled him (still clutching his hand) to a smooth, black door and unlocked it first magically and then with a small, silver key. When he opened the door, John had to stifle a cry of alarm. It was clear that someone had broken in; the room (John noticed distantly that unlike the Gryffindors, Slytherin students each had their own tiny bedrooms, though they were more cramped and hardly near as cozy as John's five-to-a-room) was in complete disarray, the small bed strewn with papers and clothes and the floor littered with a great assortment of books, quills, upturned ink, precious stones, potions bottles, dirty socks, crumpled ties, and torn up parchments.

Sherlock pulled him inside and shut the door, mumbling, "Never mind the mess," just as John was whispering, "God, what happened? Who did this?"

They both stopped and looked at each other, and then Sherlock began flinging things from the bed, stammering, "Well, obviously I can…" Clearing his throat, Sherlock kicked some things under the bed. "Straighten things up. A bit." He stabbed a penknife through some sheaths of paper lying on his small desk and John's eyes skittered to the skull beside them.

"That's a skull," he said, lamely.

"Friend of mine," Sherlock shrugged, stuffing his hands in his pockets. "Well, I say 'friend'."

That did it: John was laughing again, his eyes watering. To Sherlock's bewildered stare he rasped, "Alas, poor Yorick! I knew him." It was a weak joke, but it sent him into renewed peals of laughter anyway.

Sherlock folded his arms. "Considering the man's name was Stanley Weiss and he died in an alchemic fire in 1879, I doubt that very seriously."

John wiped at his eyes and shook his head. "Not much on Shakespeare, then?"

"Ah." Sherlock started tugging at his tie, undoing the knot with slim pale fingers. "Muggle literature. Not really my area."

Gulping, John watched Sherlock tear off his tie and realized that his own hands were trembling terribly. Sherlock certainly didn't seem to be shy about this sort of thing, for all that John had never heard anyone mention Sherlock's love life with anything more than a derisive snicker. Well, if Sherlock was marching steadily along…John took a deep breath and wriggled his own tie loose, saying in a voice that sounded an octave deeper than usual, "What is your area, then?"

"Crime," Sherlock said at once, undoing his cuffs. "Potions. Herbology. Some Muggle studies, when it suits me, though I prefer their more practical habits over whatever poetical drivel they study at Muggle school." He pushed up his sleeves and toed off his shoes, perching lightly on the edge of the bed. "Defensive tactics, both magical and Muggle. Unlike most wizards I don't consider hand-to-hand combat beneath me. The violin." Shrugging, Sherlock slid up on to the bed and pulled his knees up, wrapping his arms around them. "I'll try anything once. But if it bores me, I discard it."

That wasn't quite the answer John had expected, though it was infinitely more interesting. Pushing up his own sleeves, he sat nervously beside Sherlock, uncannily aware of the small distance between them and his urge to close it. "Conspicuously absent from your list," John said quietly, "would be 'dating'."

"I don't date." Sherlock's arms tightened around his knees.

"That's fine!" John said quickly, leaning towards him a little. "It's fine. Dating, not your area. I don't mind. Really."

"Of course it's fine." Sherlock examined John's face slowly, carefully, and John felt himself blush again. Had he been mistaken? No way. Sherlock tugging at his hand, yanking him into his room after curfew, pulling off articles of clothing…no, John wasn't a genius like Sherlock but even he couldn't mistake such obvious signs.

Right?

"Oh," Sherlock said softly, and John's stomach sank. "John…" He cleared his throat and shuffled a little, brushing the hair from his face. "I think you should know that I'm quite busy with my work, and while I'm flattered by your interest, I'm really not looking for anything-"

"Oh God," John slid off the bed and onto wobbly legs, putting his face in his hands miserably. "I'm not…oh…I just…that's fine, it's fine-"

John's speech, if the stammered fumbling he was doing could be coined as such, was interrupted by three harsh raps on the door.

"Sherlock, we need…" The door swung open and Lestrade appeared, his tired eyes raking over the room. "Oh. Sorry. Interrupting something?"

"No," they both said, a little forcefully. John looked at Sherlock, who was looking back at him with wide eyes, before deciding to studiously examine the carpet near his feet…or rather, what little patch of carpeting he could see beneath Sherlock's ungodly mess.

"Right." Lestrade shifted, cleared his throat. "Well. If I'm not-"

"You're not," Sherlock said, loudly. John's ears went pink.

"Okay. Well, then…we've got something for you."

All the tension in the room seemed to dissipate. "Another murder." Sherlock was all eagerness, slipping off the bed with all the easy grace of a jungle cat, his eyes aglow.

"Yes, another one." Lestrade sighed. "And I've been authorized to bring you to the scene, so let's go. We'll Disapparate from Hogsmeade."

Sherlock pressed his palms together and touched his fingers to his lips. "What's different this time?"

"You know how they never leave a note?" Lestrade asked, and Sherlock stared at him, unblinking, until he went on, "Well, this one did. Will you come?"

"If I can bring John," Sherlock said, his tone a little defiant. John looked up at him sharply, unable to keep the surprise from his face.

Sherlock's smile was almost soft as he stammered, "I…I work better with an audience. And I can't exactly take Mr. Weiss, can I?" Returning the smile with one of his own, John ducked his head and chuckled.

"I'm not authorized to bring _him_," Lestrade whinged, looking back and forth between them. "It's bad enough we're breaking every rule bringing you in-"

"Yes, because you need me." Sherlock stuffed his feet into his shoes and flashed a much nastier smile at Lestrade. Without looking away from the Auror's eyes, he drawled, "John, will you come?"

John looked helplessly between them and saw the exact moment the Auror let out his breath. "Oh, do as he says," Lestrade sighed, looking at John with something like amusement. "Help yourself."

"Excellent," Sherlock grinned, yanking on his coat. "Then let's go."

x

John couldn't help but study Sherlock's face in profile as the three of them marched their way down the long road to Hogsmeade village. He did think he was being reasonably sneaky with his glances, though, until Sherlock sighed and said, "Okay, you've got questions."

Flitting a look over at Lestrade's overly impassive expression, John licked his lips and decided to stick to less personal topics of conversation. "Earlier-"

"A misunderstanding," Sherlock said quickly, likewise looking at Lestrade. If anything, his face was somehow paler.

"No! God, no. I meant…at the lake." For all the colour Sherlock was losing, John felt like he was gaining it. He suspected his face must have been glowing, it was so hot. Lestrade cleared his throat uncomfortably and seemed to quicken his steps.

"Right, of course." The relief in Sherlock's voice both soothed and stirred John. They couldn't avoid the topic forever, surely, but he was glad they were going to set it aside for now. "Well. As I said, I didn't learn much. Merpeople aren't exactly gossips. But the chief informed me that I was not the first person to ask him about the lobalug poison."

"And who was the first?"

"The headmaster," Sherlock said, and Lestrade turned to look at him with sudden interest. Going on, Sherlock said, "Someone had tried to steal some of the poison from Hogwarts' personal stores. The Potions cabinet, I initially presumed, but the stuff is so carefully regulated that it must be kept in the headmaster's office instead."

"That doesn't sound like a lead to you?" John asked, scratching his head.

"No, of course not," Sherlock snapped. "If it were kept in the Potions cabinet, yes. But in the headmaster's office…it could be anyone. Someone from the Ministry, a student, a professor, a house-elf, a parent, any of the variant and random visitors our headmaster entertains almost daily…do you see now?"

"Right," John said slowly, "but you're forgetting the fact that in the headmaster's office it would have been heavily guarded, under lock and key, and probably in constant view of the headmaster at all times. Someone couldn't just…come in and snatch it up, could they?"

"Someone certainly tried." Hugging himself against the cold, Sherlock's eyes were distant as he muttered to himself, "The would-be thief visited Hogwarts in the last month, if the merman's word can be trusted. It's worth potential investigation, I suppose, but it's not enough! Looking into every single person to set foot into that office would take ages. No, there has to be some other clue. Something else…" He carried on muttering, his hands bouncing from his pockets to some wild mid-air gesticulation and then back again, until they'd finally reached the limits of Hogwarts' enchantments.

"Ready, boys?" Lestrade asked, offering each of them an arm. Sherlock eyed the proffered limb with distaste before taking it in his hand gingerly, making John's throat go tight as he remembered the easy way Sherlock had taken his hand so many times that evening. How could he have pegged things so wrong? It felt _right_, even still. But then, Sherlock's reaction… Shaking his head at himself, John brushed the thought away and looped his arm around Lestrade's. Lestrade glanced at them both, tugging Sherlock a touch closer (and making Sherlock grimace horribly) before nodding his satisfaction and saying, in a clear, brisk tone: "Lauriston Gardens!"


	6. Chapter 6

Being three months short of seventeen and raised by Muggles, John did not exactly have much experience with Apparation. Like the few times he'd done Side-Along before, he was sickened and dizzy by it, unhappily groaning as the world spun around him (or was he doing the spinning?) and then settled, with a wobble, on a dark and damp London street. He slid his arm out of Lestrade's and put his hands over his stomach, swallowing back the queasy feeling that was slowly retreating.

Sherlock, however, seemed entirely unaffected. "Come along, John," he called over his shoulder, swishing off in the direction of…nothing. There was nothing to see there. John felt the very strong urge to turn around and go elsewhere. The compulsion was so strong he could almost hear it, a soft female voice bidding him, "_Go away. There's nothing to see here. Go. Leave. Now._" John took one hesitant step in Sherlock's direction and then paused, cocking his head. What was he doing here? He really ought to go away. There was nothing to see there. He should leave. Now.

"John!" Sherlock snapped, looking exceptionally impatient, and John met his eyes with intense trepidation. He had no doubts now: there was some serious magic surrounding this place, and overcoming it would be a very challenging task indeed.

"Sherlock, I don't think-" he began, and then just like that the oddly compelling voice and the constant tug at his mind were gone, and building that hadn't been there before was suddenly looming in front of them. Standing in front of it, with her arms akimbo and her hands on her hips, was a very pretty young witch in Auror's robes, her hair wild and a scowl marring her soft features.

"Hullo, Freak," she said nastily, looking at Sherlock, and John immediately understood. Warding magic, of course. The Auror had been sending out the signal to everyone, he figured, Muggle and wizard alike. It shouldn't have surprised him that Sherlock was impervious, but he couldn't help casting an admiring look at the boy before glancing back at the young Auror. "Who's this, then?" she said, meeting his eyes.

"A colleague," Sherlock said flatly, brushing past her and towards the alarmingly worn-down old building. John wondered, with a rejoining surge of queasiness, if there were going to be any rats they'd have to shoo away from the body.

"A colleague?" the woman laughed. John decided that he liked her accent, but not her attitude, as she went on, "You're a fifteen-year-old psychopath. How do _you _get a colleague?" She turned to John and eyed him with a smarmy little smile, apparently gearing up for a bit of a diatribe.

She was halted, however, by Lestrade, who sighed and said, "Enough, Donovan. The charms, please." His tone was familiar, like a weary father scolding a pair of siblings. Donovan set her jaw and drew her wand, releasing a slow and irritated breath as Sherlock skipped up towards the steps, whistling jauntily. John listened to her mumbled spellwork for a moment before skipping along after Sherlock…until an equally smarmy looking bloke with floppy, dark hair and the sort of face that begged to be punched swaggered out of the building and stood in front of Sherlock, arms crossing like a challenge.

"Ah, Anderson," Sherlock said, a fake smile tugging at his lips. "Here we are again."

"Against the better judgment of nearly everyone involved, yes," Anderson said, his voice nasal. John took an instant dislike to the fellow despite his Auror's robes. "You should be at school."

"And you should be better at your job," Sherlock said sweetly. He then launched into a long and uncomfortable divulgement of Anderson and Donovan's personal lives (and the way they were…intertwined, so to speak) before giving them a little half-smile and sweeping into the house. John followed awkwardly behind, trying (and failing) not to stare at Donovan's knees on the way in. Lestrade, wearing a harried look on his face but staying very patiently quiet, led them stairs that wound endlessly upwards, each step creaking and groaning beneath their feet.

The house was in a sorry state. Mildewed, cracked, and peeling wallpaper lined the stairwell. The smell made John think of clothes that had been left too long in the wash, only amplified by a hundred times and spread _everywhere_. John wasn't terribly familiar with the area but he knew Lauriston Gardens to be in Brixton, which was something of a rough neighborhood. Looking at the remnants of food and filth left behind by seemingly decades' worth of squatters, John thought "rough" was probably a bit of an understatement. Despite himself, though, John found he was rather cheery. Mortified by the memory of Sherlock's bedroom, sure, and surrounded by conditions that would make his mum squeal, but generally pleased. After all, Sherlock was rambling observations about the house in his low voice just to John's right, and his leg didn't hurt a bit.

Lestrade led them up to the third floor and into a hall that looked as horrible and dank as the rest of the place. John was so busy taking in the utter shambles around him that he almost didn't notice Lestrade and Sherlock had stopped in one of the rooms until he nearly bumped into them, and peeking between them he could see why they'd stopped.

There was a body on the floor.

"Jennifer Wilson," Lestrade said as John's expression softened sadly. He hadn't seen a…a body in a long time. Judging by the expressions of the other two, though, it was the sort of thing a person could get used to. Neither of them looked even vaguely bothered by the woman lying face-down on the floor, her hair mussed and her limbs limp.

Lestrade and Sherlock squabbled for a moment (Sherlock having apparently decided that Lestrade was capable of thinking too loudly) before Sherlock took a few careful steps towards the body and examined it thoughtfully. He touched her jewelry, her coat, her umbrella, before standing up and looking intensely at the body as though he expected it to do something other than lie there on the dusty wooden floor.

"He waits," Anderson said suddenly from the doorway, and John leapt a little before turning towards him and making a face. What in the hell was the man going on about, and _why _would someone with such a weasel-like face go sneaking around like that? It's like he really was asking for a punch.

Sherlock glanced up at Anderson with a surprisingly similar sentiment on his face before striding over and shutting the door in his face, saying, "Yes, thank you, I can read." John almost smirked…except that he'd finally caught sight of what the two were talking about. Just beside Jennifer Wilson's head were the words "HE WAITS". They were scratched into the floor, and John noticed with a churn of his stomach that the woman's nails were bent and torn on her left hand and that the unfinished second curve of the final "s" bore a small but distinguishable little piece of bloodied fingernail.

"Merlin's beard," John groaned softly. He squeezed his eyes shut, only to have them startled open again by Sherlock's small barking laugh. "What?" he asked, wondering if Sherlock was going to take the piss because John was bothered.

"That's the first time I've heard you swear like a wizard," Sherlock grinned, his mirth incongruent with the scene around them. "Normally you use Muggle swears. It's oddly endearing."

John's discomfort took a different sort of slant. He cleared his throat and shot a look at Lestrade, who was staring at him like he'd only just seen him for the first time. "Endearing?" Lestrade mouthed, his eyebrows raised, and John flushed crimson. Any more commentary from Lestrade, though, was quickly washed away in the litany of observations Sherlock had made about the dead woman. She was from Cardiff, unhappily married, regularly unfaithful, and had carried a small suitcase. Sherlock went on for some few minutes, explaining- with a note of derision- how he'd come to his conclusions, and John was once again blown away by the boy's unbelievable ability.

"Amazing," he said softly. John had forgotten all about Lestrade, all about the body on the floor and the person out there killing Muggles for sport. For a singular moment, nothing existed but Sherlock, who rewarded his praise with small, slow smile. Lestrade's awkward throat clearing seemed to snap them both back to awareness, though, and Sherlock gave a little start before tapping his foot on the scratched message Jennifer had left them and saying, a bit impatiently, "It's not amazing if it doesn't help us find the murderer. This…this is our best chance. 'He waits'. What did she _mean_?"

"Don't know," Lestrade admitted, unhelpfully. "If you're done with the examination, we'll go downstairs so my people can finish up in here. All right?"

"Yes, fine," Sherlock said, waving his hand distractedly. He careened out of the room, his eyes withdrawn, and was jogging down the stairs before John had even taken one step. Feeling decidedly useless and not just a little tired, John followed more slowly behind, unhappily noting the slight twinge in his leg that seemed to appear on the second staircase.

Downstairs, Sherlock was pacing rapidly, the floor groaning. "He waits, he waits," he was whispering, trying out different inflections with each recitation. Finally he stopped and growled, "Waits for _what_?"

"Maybe it's a supernatural sort of thing," Anderson suggested in his awful, wheedling tone. "Some kind of…being."

"Right," Donovan butted in, standing in the open doorway with her arms over her chest. "Or, could be a sort of announcement. Someone big is about to cause us even more trouble, that ilk. Maybe someone who fancies himself a bit of a second You-Know-Who." At this, every Auror in the building began rumbling their concern until it seemed that the very air was stirring with worry and accusation.

. "Shut up; everybody shut up!" Sherlock cried, and the din fell abruptly to a stop. "Don't move, don't speak, don't breathe! I'm trying to think. Anderson, face the other way. You're putting me off."

"What?" Anderson said, and John had to put his hand over his mouth to stifle his giggles. "My face is?" Lestrade gave him a silencing look, and Anderson settled his features into a sneer.

"John," Sherlock said gravely, ceasing his pacing to stand right in front of the shorter boy, taking John's shoulders in his hands. His voice deadly serious, he asked, "What do you think?"

"What do _I_…" John shook his head, aware that everyone in the room was staring at them.

"Think, yes!" Giving him a little shake, Sherlock repeated, "What do you think? Quickly!"

"I…I think it's a warning!" John shrugged, the movement slightly impeded by Sherlock's strong grip. "To other Muggles, maybe."

"A warning…" At once, Sherlock released him and resumed his pacing. He stopped mid-step, his eyes going wide. "A warning…yes…but not to other Muggles…" Looking up, Sherlock blinked and said, slowly, "I need to think. I'll…be outside."

"Sherlock, are you okay?"

Sherlock looked over at John distractedly. "Yeah, yeah. I'm fine. Lestrade will get you back to the castle, John. I'll just…pop outside for a moment, won't be long." He walked away swiftly, his shoes clicking against the floor, and slammed the door behind him. John looked over at the adults, who weren't paying them a whit of attention anymore, and then crept over to the door, looking back once before slipping outside as well.


	7. Chapter 7

Sherlock was just sliding into the backseat of a cab when John made it out into the street. "Sherlock!" he shouted, but it was useless. The car door slammed shut and the cab pulled slowly away from the kerb, smoke rising lazily from the exhaust.

"No, _no_!" John looked up and down the street for another taxi but there were no others that he could see, just an expensive and shiny black sedan parked some ways down. It looked a little out of place, actually, and John stared at it for a moment before looking away, groaning. Sherlock, that idiot! John was ninety percent certain that Sherlock had figured out where the killer was hiding and had run off on his own to meet him. Imbecile! If he'd only said something to Lestrade, or at least taken _John_…

Clenching his fists, John considered his options. He could Apparate, maybe, except he wasn't allowed to do magic, had never Apparated on his own, and had no idea where he was going. A broomstick would be nice, but on a Muggle road and without a broom at hand that didn't seem a likely option. No other cabs, and Sherlock's was well out of sight…Damn it! He couldn't just stand there; he had to do something! Consumed by his thoughts, John didn't notice the sleek little car easing up alongside him until the window rolled down and a stiff, bland voice droned, "Get in the car, Mr. Watson."

John tried to peer in, but the inside of the car was somehow shadowed. "Who are you?" His voice was steady, even as the hairs on the back of his neck began to rise.

"My boss requests an audience," the voice said, the professional tone oddly chilling. "He is not used to being denied, and I fear he won't take kindly to it, sir. Get in the car."

"And who exactly is your boss?" John asked, lifting his chin a bit…though he already feared the worst. The killer, of course. The one killing Muggles. Who else?

"My boss is a man of limited patience and abundant means," the voice answered mysteriously. "For example, my boss informs me that your sister Harriet is currently at a pub in Shoreditch, and your mother is sleeping at home, though I suspect that all could change quite rapidly, if needs must. Now, I'm sure your situation is quite clear to you. In the car, Mr. Watson." The window slid back into place with a little clicking noise and John stared at his own pale reflection for a moment before swallowing hard and opening the door.

The interior of the car was magically enlarged so that John actually stepped into what looked like a large foyer, with several feet of space above him, marble floors, and a little fountain tucked into one of the corners. There was a large, plush settee in the center of the room, and leaning against one of the armrests was a strangely familiar looking man, though John couldn't quite place him. He took a deep breath and started off towards the man, an edge to his voice as he said, "If you wanted my cooperation, you ruined that the second you threatened my family. Who are you and what do you want?"

"Have a seat, John," the man said pleasantly, gesturing towards the settee. John ignored him, his jaw clenched, and the man's face shifted from pleasant to mildly irritated. John thought there was something dangerous in his eyes. The thought only made him stand up straighter. Softly, the man mused, "You don't seem very afraid."

"You don't seem very frightening," John spat, earning a tinkling little laugh from his "host".

"Oh, yes," the man smiled, "the bravery of a Gryffindor." His expression showed exactly how distasteful he found the idea, despite his apparent amusement. More seriously, the man asked quietly, "What is your connection to Sherlock Holmes?"

"Where is he?" John said at once, adrenaline singing in his veins. He was certain this man must know, though why Sherlock had left if not to hunt him down, John wasn't sure. "What do you know about Sherlock Holmes?"

The man's smile was wide and menacing. "I know a great deal about him, Mr. Watson. You might even call him my top priority." Leaning back a touch, the man sighed. "I know that you've been assigned as his mentor. But, I will admit, it is your presence alongside him at a crime scene that intrigues me. He doesn't have friends; surely you've noticed. So, who are you?"

"I'm not sure that's any of your business." Looking once around the room, John brought his stare back to the man and met his cool gaze levelly. "Why are you asking me all of this?"

"Because," the man said, dark eyes narrowed slightly, "I worry about him. Constantly."

At once, John knew exactly who he was looking at. "Mycroft? Mycroft Holmes?"

A dash of irritability swept across the man's features, quickly replaced by another sickly sweet smile. "Very good. Very clever. Yes, I wondered if you might recognize me. Now, back to the subject at hand: my brother. What is your-"

"Oh God," John gasped, and Mycroft's face darkened considerably at the interruption, only to go pale as John whispered, "If you're not the murderer…"

"Murderer?"

"Oh no! No, no…" Taking a few steps back, John's eyes widened. "Sherlock's gone off with a murderer. Mycroft! Your brother's gone off with a murderer!"

Mycroft examined John's face for only seconds before slipping a small device, which looked like a seashell in John's opinion, from his pocket and raising it to his lips. "Team Alpha," he said to the shell, his voice soft, "your twenty, please. Over."

John's eyebrows raised as the shell said, in a clear and crisp male voice, "Team Alpha, en route to undisclosed. Southbound on George Street, in pursuit of Mowgli and Unknown. Over."

"Team Alpha, what is Mowgli's current condition? Over." If Mycroft looked dangerous before, John thought it was nothing compared to the look on his face now.

"Unharmed, sir," came the response from the little shell. "Over."

"See that it remains as such," Mycroft said, his voice deadly. "Over and out."

"Yes, sir. Over and out." Looking grimly satisfied, Mycroft pocketed the little device and whipped out a Muggle mobile phone, tapping at the keys hurriedly. When he looked up again he seemed almost startled to find John still standing there. "We will follow him, of course," he explained, still looking John over carefully.

"Mowgli? I'm not sure he'd appreciate the codename," John said, despite himself.

Mycroft smiled gently. "My brother would likely miss the reference altogether, but yes, I imagine should he come to understand it he would resent it entirely." Straightening up, he sighed, "Now, if we could continue our conversation-"

"Sir." A small window had opened on one wall of the little room, and a driver was peeking through it warily. John was so thrown by the oddness of it that he almost missed Mycroft's little hiss of annoyance before the driver went on, "Comms are down, sir. I've lost Teams Alpha and Bravo. Muggle comms seem undeterred, sir."

Mycroft's hand clenched on the back of the sofa. "For all the good that does us. Sherlock has consistently refused my offers of a Muggle mobile for his own personal use." Tapping his fingers, Mycroft took a deep breath and then stiffened his jaw. "Get us to Alpha's last known location and stop the car there immediately." The driver nodded and closed the window, though Mycroft continued to glare at the spot on the wall for several seconds before returning his attention to John. "I'm afraid our chat must wait, Mr. Watson."

"I want to help," John rushed, worried that Mycroft was going to toss him from the car as soon as he was able. "I want to help find Sherlock."

"And so you shall." Mycroft strolled purposefully, but elegantly, to the door and swung it open, stepping out on to the pavement. "Come, John. If left to his own devices, my brother will almost certainly find himself in mortal peril."

John followed out behind him, not able to prevent himself from looking askance at the little black car they'd climbed out of. For all that he'd been aware of the Wizarding world since he was eleven, some magic still had the ability to throw him. He looked back at Mycroft, who was frowning into the quiet London night. "We'll canvas the area. It is probable that my team is still following him, but…John, take that street," he said, pointing off towards the darkened road that led to what looked like a small university. "I'll go this way. Should you find him…" Mycroft passed him a small, throwaway mobile. "My number is the only one programmed. Call me at the first sign, understood?"

"Yes," John agreed, already itching to run and find Sherlock. "Of course."

"Very well." Mycroft waved him off and turned back to the car, leaning into the open window and exchanging hushed words with the driver. John didn't linger. As soon as he was able, he shot off into the dark with Sherlock's name running through his mind like a prayer.


	8. Chapter 8

It only took ten minutes for John to find the right cab. He stopped alongside it, his hand on the boot, and tried to catch his breath as he fiddled with the Muggle mobile. He had one of his own, of course, that he used when he was home…but this one was a real piece of work. Expensive, John would wager, and without a single button he could see. Once he'd finally figured out how to turn the damn thing on, he fumbled with it for a moment until a frustrated groan slipped through his pursed lips.

Of course. No signal.

Bloody hell! John wasn't much of a churchgoer (Catholic mum, Protestant dad, lesbian sister: no wonder) but he found himself muttering to Providence or God or whoever, "Not going to make this easy on me, are you?" He stuffed the phone back in his pocket and looked up and down the deserted street before glancing up at the building- Roland-Kerr College, apparently- and heaving a sigh. Well, there was no use standing out in the road like a spineless git. Someone was going to have to make a daring rescue, and it looked like that someone was going to be a certain John Watson.

x

Getting into the building was surprisingly easy (never heard of locking the doors at night, it seemed, these college folk) but finding Sherlock was another matter entirely. For one thing, the place was enormous. Not Hogwarts enormous (although, to be fair, shifting staircases and randomly appearing rooms made the castle seem a bit more formidable than it really was) but still well too large for a proper and thorough inspection. John paced aimlessly through the corridors, peeking into classrooms and hissing, "Sherlock! Sherlock!" but to no avail. And what if he was too late? What if- God forbid- he stumbled into an empty classroom to find Sherlock lying on the floor in a pool of his own vomit, his neck already turning an unearthly green from the lobalug poison? The thought hardly bore considering, it was so awful, but it tugged at John so urgently that his pace quickened along with his heart and his voice became more frantic, more worried as he continued to call out: "Sherlock!"

He reached the far corner of the building and stopped in the turn, yanking the mobile out of his pocket and thumbing at it again with his mouth set in a grim line. Christ! Still no signal, and what was he supposed to do? There was no way John could search this entire building in time, not by himself. Where were Mycroft's men? If only-

"Oh, I see," drawled a heart-wrenchingly familiar voice.

_Sherlock._

John gave a little leap of joy, stopping just short of clapping his hands together. Sherlock! Alive! And…apparently rather bored, judging by his tone. That…seemed a bit off. Forgoing his plan to burst into the room brandishing his wand and crying "A-ha!", John crept carefully towards the classroom that seemed to echo with Sherlock's voice, which was now sarcastically droning, "You're a proper genius, too." John couldn't hear the man's response (only that dreadful accent and the calm demeanor that seemed at odds with what John had expected from a serial killer) but it didn't matter. He was busy anyway, testing the door to see if he could slide it open without drawing any notice.

It would seem not. The door was very firmly closed and locked, but- ah! Old building like this, the ventilation system was perfect. And that vent beside the door seemed wonderfully suited for a boy of John's slight stature.

Excellent.

x

Having appropriated a chair for the task, and having heaved himself up into the vent with only minor difficulty, John wriggled along the cool metal vents with a small grimace. It was dusty in there and the urge to sneeze was driving him 'round the twist, but an ill-timed burst of noise was the absolute last thing he wanted. Twitching his nose unhappily, John worked his way closer to Sherlock's voice.

"Bit dull, isn't it?" Sherlock was saying. John wondered, with a little rush of nerves, if the vent actually let out into the room at all. It must, it absolutely must! Focusing on Sherlock's voice, John army-crawled onward. "Targeting Muggles? I don't think I need to remind you that it's been done before, and in something of a big way."

"Got summat bigger in the works, Mr. 'olmes," the killer said with a smile in his voice. "Summat for the 'istory books, this. See, it innit just me, Mr. 'olmes, what's after Muggles. You're not the only one who enjoys a good murder. But you? You're just a boy. And they are so much more."

Light at the end of the tunnel, and John was very pleased it wasn't in the metaphorical sense. He slid down further in the vent until he was nearly touching the grille, hanging back in the shadows and observing the room below.

Sherlock was sitting at a table, leaning back in his chair and looking at the man seated across from him with interest and disdain in equal measures. The man was not what John had anticipated at all. He looked to be somebody's grandfather, for God's sake!

"_They_," Sherlock repeated, tapping his lower lip with his index finger. "Who are 'they'? An organization?"

"I'm not gonna tell you that, Mr. 'olmes," the old man said pleasantly. "This is between us two, you an' me. You ready to play yet?"

Sherlock yawned- he actually yawned!- before leaning his hands on the table and examining the old man closely. "I know why you hate Muggles. Your wife is one, yes? You never told her. When your son was born a Squib you were relieved, but your daughter…did you wait until you got her Hogwarts letter? You did. How foolish of you. And then your wife left, and she took the children with her."

The man spread his hands out in a gesture that said clearly: _you got me._ "That's good. But this business, it's not 'bout me nor my interests, Mr. 'olmes. This is all a bit o' fun, surely, but there's a bigger picture. An' you're missin' it."

"I've told you, I don't have any interest in your feeble plans for Muggle extermination," Sherlock sighed, and then to the man's expression, "or whatever ridiculous idea of subjugation you and your _friends_ have been scheming. Unless you want to tell me more about your friends themselves or show me what you did to make those Muggles kill themselves, I'll have to assume our business has concluded and, as such, let myself out."

"You won't want to be leavin' just yet," the man said softly, not smiling anymore. For the first time, John noticed a small bottle sitting in the center of the table, filled with a sea-green liquid that seemed to glow from its own inner light. The poison. "We've not even started our game."

"On the contrary," Sherlock said, his voice sounding as sharp as his brother's had been, "the game's nearly through. Which is for the best, since I'm already bored with it. Your move, cabbie. On with it, then."

_Cabbie. _Christ. That was how the man was getting his victims?

"Sherlock 'olmes, so clever. A'right, if you're so smart." The man reached into his pocket and paused, his eyes crinkled cheerfully. "This here is the best part. 'Cause you haven't figured it out yet, have you? But you will. All I have to do is this." With a flourish, he pulled out a second bottle and set it down beside the first. They looked identical, even glowing in the same exact way, and John shook his head reflexively. What was this crazy chap playing at?

The change in Sherlock was immediate and made John's stomach drop hollowly. The younger boy sat up, his eyes raking the bottles with distinct interest, and then looked up at the cabbie with eyes that were narrowed not in anger but with keen regard. "Two bottles," he said softly, curiously.

"Two bottles," the man echoed. "One for me, an' one for you. Pick the wrong one," he dragged his finger across his throat with a crooked smirk. "Pick the right one an' you get to walk out with your life an' with me a corpse. I'll even make it easy for you." With the air of a theatrical performance, the man used one stubby finger to push the bottle on the right closer to Sherlock. "Your turn, pet."

"And if I don't choose at all?" Sherlock asked, folding his arms over his chest. The man pulled out his wand with a little shrug and Sherlock rolled his eyes, sighing, "Oh, dull." He leaned back in his chair and looked closely at the bottles, and John fidgeted anxiously. The old man hadn't even taken Sherlock's wand; John could see it poking out of his back pocket! So what was he doing? It wouldn't be difficult to overpower the man and dash off. Certainly he wasn't actually going to play this weird little game.

Except he clearly was. Sherlock scooped up the potion closest to himself, holding it up to the light, and the cabbie chuckled. "Interesting," he breathed, scooping up his own bottle and unscrewing the lid with careful fingers. Sherlock spun the lid off his bottle, giving the potion a sniff, and John's jaw dropped. No, he wasn't going to…was he? No! Was he?

Sherlock tapped the glass vial once and his mouth lifted slightly on one side. "Bottom's up," he announced, his tone betraying not an ounce of emotion, and he casually lifted the bottle to his lips as the cabbie did the same.

Later, John would look back at his actions in wondering amazement, but at the time it felt as natural as breathing. He kicked the vent's grille to the floor with hardly any effort at all and dropped to the ground, his ankles smarting a little at the impact but otherwise no worse for wear. Two sets of eyes turned to him slowly, but his wand was out before Sherlock's eyes could even widen in surprise, much less the cabbie's.

"_Expelliarmus!_" John cried, wand pointed at Sherlock, and the little glass bottle flew from the younger boy's hand and clattered off in the distance with a crash and a shatter.

"What-" Sherlock began, at the same instant the old man began drawing his wand and forming the word, "_Avada_-"

Time slowed down.

The world went suddenly silent. John could hear his own heartbeat, slow and steady, and the harsh rasp of his own breath. The old man's mouth was silently forming a second word but John felt calm, unbelievably calm, as he crossed the room (why was it that he could move at a normal speed but Sherlock and the cabbie were still in slow motion?) and grabbed Sherlock around the waist, tugging him to the ground with more force, perhaps, then was strictly necessary considering the other boy was too stunned to resist.

Then time rushed back in.

"_Kedavra!_" Heartbeat thrumming wildly; Sherlock's muffled shout; hard tile and bony limbs crushing underneath him; the awful electric crack of the killing curse striking the wall with deadly force and sending drywall and wood splinters flying.

_The knife, the knife!_

John took a deep breath and time slowed once again. No time for explaining; John yanked Sherlock's trouser leg up- gaining an indignant and drawn-out "hey!" for his troubles- and withdrew the little knife Sherlock has stashed in his sock earlier. It came clean away, the sheath still tucked in Sherlock's sock, and John leapt up and flung the blade, watching it soar through the air as though underwater. The man's wand-arm was raising slowly, so slowly, but then he rocked backwards, forwards, backwards again, the knife buried in his chest. John wasn't even aware that time had resumed its normal pace until Sherlock began scrabbling up from the floor and then ran around the table, John following automatically.

They stood, one on each side, looming over the cabbie. "Was I right?" Sherlock asked, and John looked up at him, incredulous. "Was I?"

The cabbie wheezed and spluttered, his jumper darkening and the air filling with the scent of rust. John still felt oddly calm, his mind placid and his hands folded behind his back. Growling a little, Sherlock snapped, "Fine! At least tell me about your friends, mmm? Who are they?" To the man's continued silence, Sherlock gritted, "You're dying-" He lifted his foot and pressed it right up against the knife, not applying any pressure…yet. "-but I still have time to hurt you."

Distantly John was aware that he should have been horrified, or at least concerned. But that cabbie…he could have picked up John's sister, or John's mother. He could have picked up John himself, if school was out. And he _had_ picked up Sherlock. No, John didn't feel any sympathy for the man, no matter how red his face or wet his eyes. Even when Sherlock did finally press his foot down, drawing a low and awful moan from the man, John felt nothing but revulsion for him. "Tell me!" Sherlock shouted, pressing hard, and the man's mouth began to work, though only broken, choking noises came out of him.

"Let off a bit," John said. Sherlock looked at him and John shook his head, sighing, "I don't care if you hurt him, but he can't speak." Instantly Sherlock lifted his foot, though his eyes lingered on John's face for a long second before switching back to the cabbie.

"Pr-pr-pr," the cabbie gasped, and Sherlock glared at him witheringly, his foot easing back down a little. "Pro-profess-or…" He drew the last syllable out in a harsh inhale, but he never let the breath out again. He was dead.

"Useless!" Sherlock ran his hands through his hair, sending his already chaotic curls into even further disorder. "And you- you broke the bottles!"

"What?"

"You broke them!" Sherlock pointed at first one bottle, lying smashed on the ground beside the man in a puddle of hissing fluid, then the other, which had flown into a wall. "I could have examined those, you know."

"I- you- would you listen to yourself? Unbelievable!" John set his hands on his hips, fully prepared to go into a strop, but the look on Sherlock's face gave him pause.

Half-amused, half-concerned, Sherlock said gently, "Are you all right, John?"

"Of course I'm all right," John snapped, hands still on his hips.

"Well, you have just killed a man."

"Yes, I-" John stopped short, his mouth pulling into a frown. "Yes, I suppose I did."

Sherlock seemed to mentally debate with himself for a moment before stepping forward and grabbing John's shoulders. "No one will blame you. When they check his wand, they'll find the Unforgivable and they'll know you only did what had to be done. That man had to be stopped."

Making a small noise of agreement, John looked briefly away. Did it make him an awful person, that he'd just taken a life and all he could think about were Sherlock's eyes and how warm his hands felt? Feeling oddly tense, John said lightly, "Besides, he wasn't a very good man, was he? Frankly a bloody awful cabbie."

Something about Sherlock's laugh set things to rights. He squeezed John's shoulders before releasing them and sighed, before exclaiming cheerfully, "One good thing! At least we know I was right."

"Oh?"

Gesturing towards the steaming mess of potion that was corroding the college's wooden floor, Sherlock grinned, "Lobalug. I'd recognize that reaction to wood anywhere."

John cocked his eyebrow, first at the floor and then at Sherlock. "How'd you know?"

"Easy." Sherlock folded his arms, looking every bit pleased with himself. "Lobalug poison begins to crystallize at thirty-one degrees and although the crystals themselves are transparent, they do have a distinct smell. The cabbie had the bottles in his pocket for at least an hour, by my estimation, but probably much longer than that. Body heat, John. My bottle didn't have any crystals, none at all."

"And his did?"

Sherlock shrugged. "Presumably. I didn't check."

"You mad bastard," John breathed, and Sherlock looked at him with something akin to astonishment before falling into a fit of what could only be called giggles. John joined him, and the two were still cackling when a dozen or so Aurors and six men in midnight-blue fatigues burst into the room, wands at the ready.


	9. Chapter 9

The unreality of the situation seemed to settle in as John sat at one of the desks, flanked on either side by Aurors, and watched Sherlock take center stage at the front of the room. He stole a quick glance around the room, at Mycroft's "Alpha Team" who stood at the ready in a loose circle around the group and at Lestrade and his people, who were all seated and waiting with such a vast variety of expressions that John could take them in all at once. It was the single strangest moment of John's life, made even stranger by the presence of the dead cabbie, who was still lying on the floor in a pool of his own blood.

"I first realized the murderer must have some involvement in the transportation industry upon examination of the extenuating evidence," Sherlock began loftily, his hand waving imperiously and his eyes trained on the ceiling as he paced. A few stifled giggles from the group and a coughed "Sherlock" from Lestrade, however, made him grit his teeth and look at the little group crossly. "I thought he must've been a cabbie," he began again, "because nothing else made sense. The victims didn't know each other, they didn't struggle, and none of the Muggle witnesses noticed anything unusual, which means they were abducted of their own volition. Taken by choice. How does that happen? What would lead a person to climb into a car- had to be a car, Muggles would've noticed a magical disappearance and remembered it- with a stranger?"

"Seems rather obvious when you put it that way," one of the Aurors quipped from the back of the room, his face turning as red as his hair when everyone shifted to look at him.

Snippily, Sherlock folded his arms and said, "That's because it _was_ rather obvious."

"Right, and when were you planning to share that idea?" Lestrade wasn't sitting but was instead leaning against one of the desks, his mouth pulled into a thoughtful frown.

A little shamefaced, Sherlock shrugged. "Eventually. Anyway, the big break came from Jennifer Wilson and her message. 'He waits.' Anderson, being an idiot, thought it had something to do with the ever-present boogie man." His words were so drenched with sarcasm that even John felt embarrassed for the Auror, however much he disliked the man's face. "Donovan, being slightly less an idiot, thought it must be a warning about the actual murders themselves, suggesting a pattern that was reminiscent of the acts of Lord Voldemort." A collective shudder worked its way around the room, which Sherlock ignored as he drawled, "Still wrong, but not a bad guess." John lifted his eyebrows in surprise (hadn't the cabbie said there was something more at play, just as Donovan thought?) but all his attempts at catching Sherlock's eye went unnoticed as the boy went on, smiling, "Now, when I asked my colleague here, John Watson," Sherlock finally looked over at John, but John was so stricken by the attention that all thoughts of You-Know-Who drifted from his mind, "what his opinion was, he said 'a warning'. That's because John is barely an idiot at all. Of course it was a warning! But it wasn't meant for the Muggles in general, no. Jennifer was a clever old girl. It was meant for the Scotland Yard, who I'm sure she presumed would be examining her corpse." Sherlock snorted. "Poor Jenny had a misplaced faith in the abilities of her investigative team, naturally."

"Get on with it, Sherlock," Lestrade sighed, pinching the bridge of his nose.

Sherlock pulled a face and let out a huff. "Fine. It was a warning to us, that the murderer- who, let me remind you, could only be a cabbie- was waiting to see how the investigation went. Nothing strange at all about a cab lingering out in the street, especially when everyone who saw him would assume he didn't even know there was a crime scene there. How Jennifer knew he'd wait, I'm not sure, but considering how chatty the obnoxious bastard was, I'd guess he told her."

Everyone seemed to come to the same realization at once, but Lestrade gave voice to it: "So you…what? Just traipsed on outside and hopped in a cab with the killer without a care in the world?"

Standing just behind Sherlock, his back against the wall and his sleeves rolled up, Mycroft's frown deepened. Sherlock glanced back at him and turned back to Lestrade, clearing his throat. "I had to know for sure, didn't I? And besides, until…well, until certain events took place, I was never in any danger. No wizard would be!"

Spluttered indignation and bewildered disbelief seemed to be the crowd favourite. Over the noises of the Aurors, Sherlock explained with limited patience, "Once I knew it was lobalug poison he was using, I knew what potion he must have brewed and thus I knew the antidote." Rolling his eyes, he tugged a small pouch free from his shirt, the cord settling on his collar. "A bezoar. I always carry one, never know when you'll need it. See? I was _fine_."

John settled back against the chair, his heart beating uncomfortably fast. His actions that evening had been totally unnecessary and had almost gotten them both killed! And all the while Sherlock had everything entirely under control. Christ…

"Lobalug? How'd you figure that?" Anderson was frowning, rubbing his jaw.

Sherlock's eyes went wide, and even John had to give the man a look. "You're kidding, right? Please tell me you're kidding." Sherlock looked at each of the Aurors in turn and then laughed incredulously. "Tell-tale green shadowing along the jawline? You lot missed that? What must it be like in your funny little brains? Look here, even he noticed it," Sherlock pointed at John impatiently, "and he's a _sixth-year_. A student! And raised by Muggles at that; might as well have been raised by wolves."

There was an uncomfortable cough from the back of the room, but otherwise everyone's eyes carefully wandered away from John, whose jaw had snapped shut with a click and who was looking at Sherlock with something very close to murderous intent.

"Not good?" Sherlock queried, his face apologetic.

Loosening his jaw took effort. "Bit not good, yeah."

Sherlock swallowed and cleared his throat. "Ah…sorry." Everyone looked back at them with that- a bit sharply too, John noticed, as though apologies from Sherlock were as rare as victories for the Chudley Cannons.

Suddenly anxious to change the subject, John spoke with only a touch of squeakiness to his voice. "I only know about the effects of lobalug poisoning because of the project my mentor- Molly Hooper- and I worked on last year. Me and Molly both want to work at St. Mungo's in the future, although she's got her heart set on post-mortem, so we spent the year studying fatal magical maladies. Lobalug, uh, came up. In our research."

"What house is she in?" Sherlock asked, eyes sharp with intrigue.

"Hufflepuff."

Sherlock made a face. "Oh, gross."

"Right, if we're done with the matchmaking," Lestrade said uncomfortably, no doubt remembering the scene he'd came across earlier in Sherlock's bedroom, "I'd like to wrap this thing up." He had the boys give him a full account of what happened in the classroom, though John followed Sherlock's lead and pretended he didn't know anything about the man's supposed 'friends' or future plans, and at long last he sent them- along with Mycroft and his security detail- away.

They didn't make it very far.

Just before they reached the main entrance, John felt a pair of rough hands grasp his shoulders and tug him into an empty classroom. He struggled, and from the sounds of it Sherlock was doing the same, but it was no use; the man holding him was much too strong. Still, he kept on fighting until the light clicked on and he realized that Mycroft was standing at the front of the room, a burly guard on either side of him and a quietly displeased expression on his face.

"Let us go," Sherlock spat. He looked a bit like a cat that didn't want to be held, squirming and bristling with his pale eyes narrowed. The man holding him was trying not to smile and doing a bad job of it, the corner of his mouth twitching and his eyes crinkling. At that, John relaxed. Surely if Mycroft was going to have his men kill them they'd be a little more serious about it.

"Not until you tell me the rest of the story, Sherlock," Mycroft said, his voice soft. He wasn't smiling, not even a little.

Sherlock stopped floundering, but only so he could deliver a particularly icy glare. "Beyond what John and I told Lestrade, there was nothing of import."

"I will decide which facts are important," Mycroft said. He took a step forward, his eyes hard and glinting. "Need I remind you that obstructing the Ministry in a matter of national security could earn you a term in Azkaban?"

"Mummy would kill you," Sherlock sniffed.

Looking very put upon, Mycroft inspected his nails. "Mummy would have to understand," he said, but it sounded very weak. More sharply, he added, "I know you've left something out, brother dear. Why not make this easier on us both? I should hate to have need of my more…persuasive tactics."

John stiffened, his throat going dry, and Sherlock did the same. "You wouldn't dare," Sherlock whispered, and Mycroft's response was a sickly sweet smile. His jaw clenched, Sherlock seethed, "Fine! Go ahead! She'll read about it in the papers, anyway."

Wait, what?

"You and I both know how easy it would be for me to prevent that, brother mine," Mycroft said, a hint of a genuine smiling tugging at his lips. John looked from him to Sherlock and back, utterly confused. "You give me the information I require, and I shall make sure Mummy never hears of this little transgression. An even trade, I should think."

"Wait," John said, shaking his head. "That's what you're worried about? Upsetting your mum?"

"Shut up, John," Sherlock said, trying to look smug and instead just looking pained.

John laughed until tears were rolling down his cheeks. When at last he had himself under control, he managed, "Well, go on, then. Hate to have Mummy send you a howler," wiping the tears from his cheeks as best as he could with the brute behind him holding his arms.

Sherlock scowled at him, and then scowled at the guard when he was prevented from crossing his arms, before finally turning his scowl towards the eldest Holmes. "Fine. There isn't much to be going on with, I'm afraid, but it seems a professor at Hogwarts has taken on a rather villainous bend of late and is planning on enslaving the Muggle populace at some point in the near future. Now can we please go? I have class in the morning."

"What?" John looked at Sherlock with round eyes. "When- how- _what_?"

"Any estimation as to which professor might be so inclined?" Mycroft asked, as if John hadn't spoken.

"None whatsoever. My initial instinct would be Professor Burley, as he's the most knowledgeable in regards to potions, but since the man is Muggleborn himself I find it very unlikely. We're probably looking for a pureblood- matches the rhetoric- and it's very possible that he or she isn't working alone. Probable, in fact."

"There, now," Mycroft said, his smile subtle but obvious enough that for him it was nearly a grin. "That wasn't so difficult, was it? Now, how would you boys prefer to travel? I know how much you like the Floo network, Sherlock; any chance to get your hands dirty…"

"Apparate us to Hogsmeade," Sherlock said irritably. "We'll walk the rest."

Mycroft made a small motion that was almost, but not quite, equivalent to a shrug. "Very well." He nodded at the guards, who released the boys at once, and then placed himself between them, taking their arms. Sherlock made a small, resentful noise at the contact, but before John could snicker or even frown at the arm that he looped around his, the world was spinning horribly and his insides were wobbling.

x

With his feet back under him, John opened his eyes (without really remembering closing them) and blinked at his surroundings. Mycroft and Sherlock were bickering about something, Christmas plans by the sound of it, and John was glad they let him have a moment of peace to get his stomach settled. The moment was all too short, though, and brought to a close by Mycroft's firm gaze settling on his own.

"John," Mycroft said, looking at him intently. He didn't thank John, nor did say anything reproving or questioning or even fond, but in that look it almost felt to John as though he had. With a small nod, Mycroft looked back at his brother and said, "Good night to you both," before disappearing in a crack of air.

John blinked at the space which Mycroft had just occupied (it still blew his mind, in a way, that people could do such a thing as Disapparate) until he felt warm, slender fingers interlock with his own. He looked down at Sherlock's hand and back up, sure that his embarrassment from earlier and his worry for Sherlock were showing all over his face. But instead of looking smug, Sherlock just looked a bit sheepish. "My brother," he said, a half-smile crooking his lips. "He has a flair for the dramatic."

Laughing, John let Sherlock lead him towards the castle. "Well, thank God you're above all that!"

Sherlock nudged him with his elbow and yawned. "I should thank you," Sherlock said. "You didn't have to come looking for me."

"And you didn't have to run off without telling anyone," John admonished, still feeling chagrinned about it. "If you'd told me you had everything under control, I wouldn't have made such a muck of things." Sherlock gave him a questioning glance, and he sighed: "The bezoar. If I'd known-"

"Oh!" Sherlock laughed. "No, I was lying. There are dozens of good potions that use lobalug, all of which cause that greening effect. And none of which can be cured with a bezoar. Good trick, though. Got everyone off my back."

John stopped walking. "You're…you're absolutely barking mad."

"Oh, sure, but everyone loves a mad genius," Sherlock grinned, and John was struck with the very strong and very thorough compulsion to wipe that grin away with a kiss. He very nearly did, as stupid as the idea was, but then Sherlock was yawning and tugging him towards the castle again, mumbling about his six a.m. Potions class even as dawn was beginning to lighten the sky, and John gave it up as lost cause, following Sherlock and taking far too much satisfaction from the soft rub of Sherlock's palm against his own.


	10. Chapter 10

The headmaster had been informed of the boys' whereabouts and the importance of their involvement had been pressed upon him, so when they reached the castle doors Pontius Filch was there waiting for them, only slightly jeering, with his three hideous and scrawny cats winding around his legs. "To yer beds," he spat (literally; phlegm seemed to shoot from the man's mouth each time he opened it) and at Sherlock's quick and biting, "Obviously," he only made a face and pulled the doors shut behind them, his arms crossing and his eyes squinted at them suspiciously.

Sherlock gave John's hand a small squeeze and let go, yawning again. "A good case," he said, his voice rough, "always puts me in mind for a nap."

"It's nearly five," John chuckled. "So I think a nap is all you'll be able to manage. I don't have class till after ten, thank God."

"Oh joy, you've rediscovered Muggle blasphemy." Sherlock shook his head and sighed, "Good night, John."

John's lips shifted into a very small smile. "Good night, Sherlock." They hesitated for a moment before Sherlock nodded and turned away, stretching his back as he walked. John watched him go, eyes trailing from the mess of dark hair down to his upturned collar and the long line of his coat, and shook his head at himself before heading up to the Gryffindor tower for a much needed kip in his dearly missed bed.

x

Herbology was torture, especially with it being mandrake season, but by lunch John had finally left his grogginess behind and entered the Great Hall with inscrutably clean hands (because, truth be told, the little buggers in the potted plants made John feel more squicky than he was willing to admit aloud) and a rumbling stomach. His feet led him automatically towards the Gryffindor table, where his friends were eyeing him curiously, but a sudden shout of "John!" stopped him in his tracks.

Just that voice was enough to make John's stomach do flip-flops. _You are well and truly done for, Watson,_ John thought mercilessly, looking over at the Slytherin table. But it was true, and looking at Sherlock with his sleep-rumpled hair, impossibly tidy clothes, and perpetually sly grin only drove the fact home: John was a goner, he was royally wrecked, done in and made a lost cause. Nothing in the world could have stopped him changing course and falling on to the bench beside Sherlock just then, not even a parade of veelas wearing dresses made of Galleons. He was madly, irrevocably smitten with the madman beside him, and he was all too aware of how hopeless his chances were.

"Morning," the madman yawned cheerfully, and John was so caught up in his whirl of thoughts that he didn't even think to correct the boy and remind him it was early afternoon. "Sleep well?"

"Mmmf," John said, and then shaking himself, "Um, yeah. You?"

"Ugh, sleep. Boring at the best of times." Sherlock looked up at him suddenly, scrutinizing him carefully. "All right, you've got something on your mind. Out with it."

Damn. John cleared his throat and cast around for something, anything to talk about. "Oh, ah…the um, thing with your brother," he said after a moment, nearly sagging with relief when Sherlock accepted the topic with a raise of his eyebrow and a careful nibble of buttered bread. "Was all of that true?"

"Yes," Sherlock said, his mouth full. "But we musn't talk about it here. Later, though." He finished chewing and took a drink of cider before continuing, "Later we can discuss our plans." If Sherlock noticed John's sudden look of surprise, he didn't acknowledge it, instead grinning and saying, "Oh! But I have devised one plan that I think will please you."

"Oh?" John croaked, shifting in his seat.

"Mm. I've figured out what we're going to do about that Inter-House Challenge."

"Oh." That wasn't really what John had expected, and he was both relieved and disappointed to hear it. "Okay. What do you have in mind?"

"The cases, John!" Sherlock's eyes were glistening in a way John had already learned to feel wary about. "Why do anything more? We'll work whatever cases come my way this year together, and you'll write them up for your report. I'll…slap-dash together some sort of presentation for my O.W.L.; it hardly matters." Flapping his hand impatiently, he drawled, "I have absolutely no interesting in winning the cup, and I certainly don't imagine I'll get anything less than an 'O' for my efforts."

Actually, that was a pretty great idea. John liked writing, not that he'd ever mentioned as much to anyone else, and he'd hoped Sherlock would ask for his help on more cases. It seemed like a really tidy solution to a problem that had somehow slipped his mind entirely. "Brilliant," he said. "That's brilliant." Sherlock beamed at him so powerfully then that John had to look away and stare down a plate of delicatessen just to keep from making himself into a fool.

x

Sherlock wasn't at supper, but the Gryffindor table kept John occupied well enough, pummeling him was a barrage of questions that faded suddenly when a large, all-black owl swooped neatly overhead and dropped an envelope and a small pouch on the table before him. The envelope was a dark, rich chocolate brown, and when John opened it he found one small page of buttery-smooth, cream-coloured paper inside. Unfolding it, John discovered only a few short lines of neat, curling text written in silvery ink.

_Baloo:_

_Please allow me to extend my gratitude and apologies with a small gift. To avoid incurring Mowgli's wrath, you might consider destroying this letter at once._

_Sincerely indebted,_

_M._

John grinned at his new code-name for a long moment before suddenly remembering the little pouch and turning his attention to it at once. The pouch itself was a rich purple velvet, but once he turned out the contents into his palm the pouch fell, forgotten, to the table.

In his hand, John held two of the little shells Mycroft had used to contact his team. They really were just seashells, it seemed, but he didn't dare test them at the table. Instead he tucked them into his pocket, shivering with delight. It was almost like playing James Bond.

x

"Oi, Watson."

John looked up from where he'd been turning down his blanket to find Mike Stamford leaning in the open door of the boys' dormitory, his chubby face pink and smiling. He straightened and made a questioning noise, though the look on Mike's face was almost enough of an answer.

"Got a visitor," Mike said, and then John was sure.

Still… "Sherlock Holmes?"

"Good guess," Mike laughed. "He looks well out of place up here, I'll add."

"He's not…_in _the tower, is he?" John tried, and failed, to picture Sherlock in the Gryffindor common room.

"Merlin, no. He's out in the hall."

They shared a laugh, and Mike shook his head as they went down the stairs together. "Wouldn't have guessed it before, but you know? Something about the two of you being friends makes sense to me."

"Don't get all soppy on me, Mike," John joked, rolling his eyes. The bigger boy chuckled heartily before wandering back over to the heated gobstones tourney taking place in front of the roaring fire, and John steeled himself before stepping through the portrait and out into the hall.

"I've been out here for _ages,_" Sherlock complained immediately. He looked tired but lovely, his odd-coloured eyes hooded with drowsiness. "Suppose there were an actual emergency?"

"I've got just the solution," John smiled, remembering Mycroft's gift. He fished one of the shells out of his pocket and pressed it into Sherlock's waiting hand.

Sherlock tutted. "Mycroft, the weasel." Looking up at John, he said, "Don't let him charm you away with gifts and flattery, John. You're on my side."

John flushed a little but nodded. "No worries there, mate," he said, and instantly regretted saying. Clearing his throat, he added, "Anyway, I've got one too. So…"

"No, this is perfect," Sherlock said with a little, crooked smile. "I've been elaborately planning how to talk to you privately all day. I devised a code, and system involving the fireplaces, and this thing with a set of Exploding Snaps and a pair of sturdy owls- anyway, this is much simpler. You don't mind me hanging on to it?"

"Not a bit."

"Excellent. Then I'll be in contact. Good night, John." Glancing surreptitiously down the empty corridors, Sherlock seemed suddenly awkward. "I…well, good night." He started to walk away and John reached out automatically, grabbing his hand.

"Sherlock…" There didn't seem to be enough air this high up in the castle. Sherlock's eyes were focused on John's with an intensity that John wasn't sure how to interpret. Feeling foolish, he let Sherlock's hand go and rubbed at his neck. "Um. Good night."

There was a long pause, and then Sherlock nodded and trotted off down the hall with nothing less than his usual grace, leaving John to bumble speechlessly back up to his bed.

x

"Holmes to Watson, over."

John groaned and blinked at his bedside table blearily as Sherlock's voice, small but clear, said, "Holmes to Watson, do you read? Over." Letting out a long breath, John scooped the little shell up and brought it to his lips, whispering, "Watson here. Do you have any idea what time it is? Over."

"Oh-four-sixteen. Over."

Christ. John rolled his eyes. "That was rhetorical. What do you want? Over."

A pause, and then, "Were you sleeping? Over."

"At not quite dawn?" John yawned and rubbed his eyes. "Amazingly, yes. Yes, I was. Over."

"Oh." Sherlock sounded almost contrite. "Well, now you're awake. Do you want to me to explain that conversation with my brother or not? Over."

Despite the early hour, John found he was intrigued. "Give me a few minutes. I've got to pop to the loo. Over."

"Bring the shell with you. Over."

"Sherlock!" John had to cover his mouth to stifle a giggle. "No. That's…no. Over."

"I have no interest in listening to you urinate," Sherlock drawled, and John could practically hear him rolling his eyes. "But I've only just remembered that you share a room and it wouldn't do for any of this to be overheard. Over."

"Fine, okay. I'll call for you in a couple of minutes. Over and out." John eased out of bed and yanked on his dressing gown as he toed on his slippers, heaving a mighty yawn as he shuffled down the stairs. There was a separate annex that held both a girls' and boys' lav just off the common room, for times when the students weren't meant to be out in the corridors. John tended to his morning routine with a touch more energy than usual before sinking down onto one of the cool marble sinks and pulling the shell out of his pocket again. "All right. I'm back. Over."

"You're supposed to say 'Watson to Holmes'. It's good protocol. Over."

John smirked at Sherlock's tone, the mix of petulance and amusement clear even through the tiny shell. "I suppose we'll be using the phonetic alphabet as well. Over."

"Not a bad idea, John! Do you know it? Over."

"Learned it in scouts. Over."

"Muggles and their strange rituals. Which brings us to our topic. Over."

John's smile faded. "Yeah. How did you know all of that? Over."

"The cabbie's last word was 'professor'. Someone tried to break into the headmaster's potion stores. Do you really think that's a coincidence? Over."

"No, I suppose not." John rubbed his jaw absently, musing. "But you said it was useless. The cabbie telling you 'professor'. Threw a little tiff if I recall correctly. Over."

"That was hardly a tiff, John. We'll need to work on your memory. But no, it _was_ useless." Sherlock sighed. "I already suspected the professors, of course. I said that, remember? It could have been anyone with access to the headmaster's office." After a pause, he added, "Over."

John shrugged at his own reflection. "Narrowed the field at least. Over."

"The professors would have been my first points of investigation, obviously," Sherlock snorted. "Now, if he'd given me a name…" He sighed. "Still. This will be an interesting challenge. Over."

Taking something of a risk, John asked, "What are we going to do? Over."

There was a smile in Sherlock's voice as he answered, "I have no idea." After a moment, he said, "But you should go back to bed. I'll think on it for a bit and we can talk it over later. Over."

"Oh, you mean you'll actually keep me up to date this time? Over." John's voice was more teasing than stroppy, but he still wanted some form of reassurance.

"I have every intention of doing so," Sherlock answered cheerily. It wasn't a firm 'yes', but John suspected that was the best he was going to get, so he didn't argue when Sherlock said, "Now go to bed. I'd forgotten ordinary people sleep, and I assume you need it. Over and out."

"Yes, sir," John smiled. "Over and out." He looked fondly at the little shell and tucked it in his pocket before sighing at his own ridiculous expression. "You're done for, mate," he said to himself, shaking his head. "Well and truly."

**A/N: Thanks for reading! Any inaccuracies are due to me being too lazy to do proper research. Legwork, ugh. I should add that the entry for lobalugs is actually quite small in Fantastic Beasts and Where to Find Them, and thus I've embellished upon the idea pretty thoroughly. Here's hoping J.K. doesn't come out with something on Pottermore in a few months/years/eons that completely ruins my story. Also any dialogue lifted from ASiP belongs to Moffat and Godtiss and blah blah blah, you know the rest. Stay tuned for the sequel, "The Blind Goblin," in which John visits Gringott's for the first time, gets a beard- ahem, girlfriend- and learns a little about Sherlock's past (as well as all that smuggling jazz). **


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